Have you ever wondered why a water droplet rolls around on a hot pan instead of evaporating instantly? The part of the droplet touching the pan does indeed evaporate. The resulting vapor forms a thin insulating layer that enables the drop to hover over the pan for seconds, even minutes. This is known as the Leidenfrost effect. Because they also produce vapor when heated, sublimable solids (solids that skip over the liquid phase and directly produce vapor) also exhibit the Leidenfrost effect. This effect has been studied extensively for both liquids and sublimable solids.
Have you ever used a heat-shrink tubing at home to seal an exposed wire? As it’s shown in Video 1, you would place the tubing around your wire, apply heat, and voilà! The tubing shrinks and tightly wraps itself onto the exposed wire, and you don’t have to worry about an electric shock anymore. This type of material that changes its shape upon increased temperature is called a shape-memory polymer. Since its commercial development in 1962, scientists have found this type of material so useful that its popularity rose, especially in the biomedical and aerospace fields. However, it comes with a few drawbacks: applying the desired temperature uniformly can be tricky and the shape change induced by the heat can be quite slow. In addition, changing the temperature isn’t ideal for biological applications where the environment surrounding the material is sensitive to heat, such as in tissues and living cells. In today’s post, I’ll introduce you to a different type of shape-memory material that “remembers” its temporary shape when subjected to a magnetic field, instead of heat.
I am writing this as I embark on a journey from Copenhagen to Chicago for a 24-hour experiment. Luckily, I am going to be in the city longer than I will be flying, but only just. Traveling over 4,000 miles may seem like a long way to go for an experiment, and it is. I perform small-angle scattering experiments for a living though, and sometimes this is just what needs to be done. My previous post on Softbites was all about the fundamentals of X-ray and neutron scattering, but I didn’t give an indication of what an experiment is actually like. This post focuses on the practicalities. What are the experimental facilities like? What do you have to do to access them?
Imagine yourself as a small fly called a midge (shown in Figure 1a). You used to live in a lake as a small larva with no concerns in life except swimming, eating, and growing. One day, you hid underwater and formed a cocoon around your body as it developed wings, legs, and antennae. A few days later, you swam to the surface and burst out of your cocoon as an adult fly -- a male. As a new adult male, you find the clock ticking – you have only a few days to find a mate before you die.
If we could shrink a submarine down to the microscopic scale, could we pilot it into the human body to fight infection and perform surgery? Despite suggestions from futuristic sci-fi such as “Fantastic Voyage”, “Honey, I Shrunk the Kids”, “The Magic School Bus”, “Power Rangers”, and “Rick and Morty”, we cannot survive such shrinking and our vessel would be without a pilot. But it may still be possible to “shrink” down some of our technology and control it remotely as we will see from researchers at MIT in this week’s paper.
Many consumer products, such as clothes and food packaging, are made of blends of polymers, long molecules consisting of repeating chemical units. The attractiveness of using blends of different polymers arises from the engineers’ desire to combine multiple unique properties of each individual polymer, such as transparency, stretchability, and breathability, into a seamless whole. However, different polymers are not necessarily miscible, a term scientists use to describe whether two materials mix at the molecular level. Miscibility isn’t a one-and-done kind of deal: scientists and engineers have known for years how to make polymer blends mix by careful temperature control. What if there were conditions other than temperature to achieve polymer blend miscibility? This may ultimately help in industrial processing of polymer blends. In this week’s paper, Professors Annika Kriisa and Connie B. Roth from Emory University in Atlanta, Georgia, explore the mixing dynamics of two polymers by using a strong electric field.
When an experiment doesn’t behave the way we expect, either our understanding of the relevant physics is flawed, or the phenomenon is more complicated than it appears. When a theoretical prediction is off by two orders of magnitude - like what was observed in this recent paper by Hua Yung Lo, Yuan Liu, and Lei Xu of the Chinese University of Hong Kong - something is seriously wrong.
Scientists often draw inspiration from biological organisms to describe phenomena, even when they are studying outside the realm of biology. Physicist Pierre-Gilles de Gennes was no exception. In 1971, after being inspired by the movement of snakes, he proposed reptation theory, or the reptation model, which has since been widely used to describe motions of polymers. As the name “reptation” suggests, de Gennes assumed polymer chains move like snakes. As shown in Figure 1, the model describes a polymer chain’s motion in an environment that is highly populated by other chains (shown in gray) by assuming that the chain is confined in a virtual tube (shown in red) formed by surrounding polymer chains. According to reptation theory, the chain wiggles through this tube, similar to a snake slithering through the woods. As one might imagine, directly imaging the snake-like slithering of polymers is a challenging affair; however, in today’s study, Maram Abadi and coworkers from King Abdullah University of Science and Technology were able to do just that with DNA chains – an example of a polymer – and compared their results to prevailing theory.
If you ever played tug-of-war in elementary school, you might remember that it isn’t the friendliest game. People fall over, hands get burned from holding on to the rope, and knees get scraped from falling on the ground. Although victory can be sweet, the injuries that come with it may make you never want to play the game again. Perhaps surprisingly, there is a similar ‘’tug-of-war” happening inside your body, as individual cells move around from one place to another in a process called cell migration. What’s more, this microscopic tug-of-war may help to heal those scrapes and bruises that happened in elementary school, and those that happen in your everyday life.
In my previous post on soft nanoparticles, you were introduced to polymer-based nanoparticles that could be used in biomedical applications, one of which is cancer therapy. These nanoparticles have a range of useful properties for cancer treatments, including their spherical shape and small size (~100 nm), both of which are similar to exosomes, small globules that are used in nature for transferring proteins between cells. Since cells naturally absorb exosomes, artificial particles with this size and shape should also be easy for cells to absorb, which means these particles could be used to deliver drugs into cells. While this idea sounds promising, it hasn’t worked out in practice -- when drug-loaded polymer-based nanoparticles were injected into a tumor, subsequent tests showed that less than 1% of the injected dose entered the cancer cells. Since these particles were the correct size and shape, why didn’t they get inside the target cells?